It is well known to stabilize plastics, e.g. olefin polymers, against degradation due to heat and oxidation by incorporating into the polymers a stabilizing amount of hindered phenolic antioxidants. However, such antioxidant stabilizers have not proved entirely satisfactory for many end uses. This is true because of the relative ease with which they can be extracted from the polymers by nongaseous fluids. For example, a plurality of individual plastic insulated wire are encased in plastic tubing to form underground cables. The void spaces within the tubing are filled with a very high viscosity liquid such as petrolatum or petroleum jelly. A serious disadvantage to the use of plastic materials as insulators for this application has been the fact that at least a portion of the stabilizing amount of the antioxidants incorporated into the plastic insulation is extracted into the petrolatum. This causes a rapid deterioration of the insulation due to the combined effects of heat and oxidation.
A prior art solution to this extraction problem involves the use of novolac resins of high molecular weight as primary antioxidants. These thermoplastic resins, which are condensation products of a phenol with an aldehyde, do exhibit much greater extraction resistance than non-polymeric phenolic antioxidant or novolacs of relatively low molecular weight, e.g. those having on the average 20 or less phenolic ring groups in the molecular structure. However, commercialization of these high molecular weight novolacs as stabilizers have not been altogether successful. One reason therefor is that resins stabilized with novolacs in general tend to smoke excessively and even seriously degrade at temperatures often encountered in extrusion of the resin, e.g. in the extrusion of wire or cable coatings.
Another serious disadvantage to the use of plastic materials, e.g. polyolefin resins, as insulation for wire and cables is the fact that the degradation of the polymer is accelerated by the presence of copper and alloys of copper. Prior art methods to solve this problem have resulted in a combination of the polyolefin resin with the primary hindered phenolic antioxidant and a copper deactivator of chelating agent such as organic hydrazide or hydrazine compounds. However, these methods do not solve the problem when the resulting compositions are contacted with petrolatum. In fact, test results have indicated that the deactivation due to copper is often accelerated even further after the polymeric material has been subjected to extraction with petrolatum.
It is therefore a primary objective of this invention to provide a novel hindered phenolic antioxidant compound which exhibits resistance to extraction with hydrocarbons such as petrolatum.
It is another object of the invention to provide a novel extraction resistant stabilized polyolefin composition.
It is a further object to provide a polyolefin composition useful in underground wire and cable applications.
Other objects of the invention will become apparent from the detailed description and appended claims.